1. Field of Invention
The present invention relates, in general, to a transmission for a vehicle, and, more particularly, to a structure of a transmission for a vehicle, capable of realizing forward 10-speed and reverse 4-speed gear ratios.
2. Description of Related Art
FIG. 1 shows a structure of a conventional forward 10-speed and reverse 3-speed transmission. The transmission is made up of a first compound planetary gear train CG1 having a first planetary gear train PG1 and a second planetary gear train PG2, and a second compound planetary gear train CG2 having a third planetary gear train PG3 and a fourth planetary gear train PG4. The first planetary gear train PG1 is made up of a first sun gear S1, a first carrier C1, and a first ring gear R1. The second planetary gear train PG2 is made up of a second sun gear S2, a second carrier C2, and a second ring gear R2. The third planetary gear train PG3 is made up of a third sun gear S3, a third carrier C3, and a third ring gear R3. The fourth planetary gear train PG4 is made up of a four sun gear S4, a four carrier C4, and a fourth ring gear R4. The first ring gear R1 and the second carrier C2 are permanently connected to each other, and are integrally connected to the third sun gear S3.
Further, the transmission is equipped with: a first clutch CL1, a second clutch CL2, and a third clutch CL3; a first brake B1, a second brake B2, a third brake B3, and fourth brake B4; and one one-way clutch F1. An input shaft IN is input by means of first to third clutches CL1 to CL3, and an output shaft OUT is connected to the third ring gear R3 and the fourth carrier C4.
The conventional 10-speed transmission as mentioned above realizes forward 10-speed and reverse 3-speed gear ratios by means of a combination of components as shown in FIG. 2, and a lever diagram thereof is shown in FIG. 3.
In the conventional transmission configured as mentioned above, the rotational speed of the second sun gear S2 is frequently excessive. As a result, the efficiency of power transmission is reduced, and the durability of related components of the second planetary gear train PG2 such as a pinion gear, a pinion shaft, and a needle roller bearing, is reduced.
That is, referring to FIGS. 2 and 3, in the 4-speed and 6-speed gear ratios in which the second clutch CL2 and the second brake B2 are operated at the same time, the rotational speed of the second gear S2 is excessively high.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.